The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Atrial fibrillation is a form of cardiac arrhythmia where there is disorganized electrical conduction in the atria causing rapid uncoordinated depolarizations that result in ineffective pumping of blood into the ventricle and a lack of synchrony. During atrial fibrillation, the atrioventricular node receives electrical impulses from numerous locations throughout the atria instead of only from the sinus node. This overwhelms the atrioventricular node into producing an irregular and often rapid heartbeat. Due to the lack of organized contraction of the atria, blood may pool in the atria increasing the risk for blood clot formation. The major risk factors for atrial fibrillation include age, rheumatic heart disease, valvular heart disease, hypertension, diabetes, coronary artery disease, and thyrotoxicosis. Atrial fibrillation affects about 7% of the population over age 65. At present there are over 6 million patients affected with atrial fibrillation (AF) only in the US. It is estimated that by 2025 over 10 million patients will have atrial fibrillation. AF is the leading cause of strokes and is the most common arrhythmia leading to hospital admissions.
AF may be intermittent (paroxysmal) or persistent. It may be acute and terminate within a relatively short period of time, or it may be chronic and persist for years. AF may develop in patients with structurally normal hearts as well as in patients with associated comorbidities including structural heart disease. Based on the presence of clinical characteristics and comorbid conditions, patients with AF are at variable risk for stroke and other thromboembolic events. Therefore, based on the degree of risk of stroke, patients are treated either with antiplatelet or anticoagulant agents to reduce the risk of stroke. However these agents, on the other hand, do increase the risk of bleeding complications, including intracranial risk. Therefore, in patients with AF, risk of thromboembolic events, particularly stroke, compete against the risk of bleeding complications due to antiplatelet/anticoagulant agents. To optimize these competing risks, it is desirable to accurately identify when patients with a history of AF go into AF and how long they stay in AF.
AF treatment options are still evolving. In most patients restoring and maintaining sinus rhythm is preferred, as sinus rhythm is often associated with an improvement in quality of life, improvement in atrial and ventricular remodeling with an improvement in ejection fraction, possibly a reduction in the risk of thromboembolic events, and elimination of the need for anticoagulant therapy in most patients. Cardioversion attempts to restore sinus rhythm; yet even if successful acutely, AF may still recur as cardioversion does not eliminate the underlying mechanisms of AF. In addition, if there is a blood clot in the atria, cardioversion may cause the clot to leave the heart and travel to the brain (leading to stroke) or to some other part of the body.
One of the more recent procedures for treating cardiac arrhythmias is catheter ablation therapy. Physicians make use of specialized ablation catheters to gain access to interior regions of the body. Catheters with tip electrodes or other ablating devices are used to create ablation lesions that physiologically alter the ablated tissue without removal thereof, and thereby disrupt and/or block electrical pathways through the targeted tissue. In the treatment of cardiac arrhythmias, a specific area of cardiac tissue having aberrant electrically conductive pathways, such as atrial rotors, emitting or conducting erratic electrical impulses, is initially localized. A user (e.g., a physician) directs a catheter through a main vein or artery into the interior region of the heart that is to be treated. The ablating element or elements are next placed near the targeted cardiac tissue that is to be ablated, such as a pulmonary vein ostium or atrum.
While the available treatment methods provide various degrees of success, it is nonetheless difficult, at times, to determine the effectiveness of the treatment. Part of the difficulty arises because care professionals will typically rely, even partially, on the patient's perceived state of health to gauge effectiveness. Patients naturally have varying levels of perception; and moreover a patient may experience atrial fibrillation and not know it. This problem is in fact heightened after a medical procedure, when the patient has returned to normal life, and may begin experiencing atrial fibrillation while feeling as those their heart function is normal. Up to one-third of patients with AF do not appreciate or know that they are experiencing AF; and therefore, they do not know they are at heightened risk for stroke. It is, therefore, desirable to have an effective mechanism to measure atrial fibrillation that is cost effective and consistent in operation.